CN111137869A - Preparation method of lithium iron phosphate - Google Patents
Preparation method of lithium iron phosphate Download PDFInfo
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- CN111137869A CN111137869A CN201911354208.2A CN201911354208A CN111137869A CN 111137869 A CN111137869 A CN 111137869A CN 201911354208 A CN201911354208 A CN 201911354208A CN 111137869 A CN111137869 A CN 111137869A
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/04—Construction or manufacture in general
- H01M10/0422—Cells or battery with cylindrical casing
- H01M10/0427—Button cells
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- H—ELECTRICITY
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Abstract
The invention belongs to the technical field of recovery and recycling of battery materials, and particularly relates to preparation of lithium iron phosphate. The method for preparing the lithium iron phosphate by the crude lithium phosphate obtains a pure lithium solution by stirring and washing, acid dissolving, phosphorus removing and step-by-step impurity removal, then adds an iron source, a phosphorus source and a carbon source, and obtains the lithium iron phosphate by mixing treatment. The preparation method disclosed by the invention has the advantages that the loss of lithium is reduced to the minimum, the recovery rate of lithium is more than 99%, the high-purity and good-performance lithium iron phosphate is obtained by taking low-cost rough lithium phosphate as a raw material, a phosphate byproduct generated in the reaction process is used for other purposes, and only a small amount of waste liquid and waste residue are generated, so that the production cost is reduced, the preparation method is environment-friendly, and the preparation method has a good application prospect.
Description
Technical Field
The invention belongs to the technical field of recovery and recycling of battery materials, and particularly relates to a preparation method of lithium iron phosphate.
Background
Lithium iron phosphate is a widely used lithium ion battery cathode material, has become a preferred cathode material for batteries of electric vehicles, power batteries and energy storage batteries due to excellent safety and long cycle life, and plays an increasingly wide role in the field of new energy industry.
At present, with the further development of the lithium ion battery industry and the maturity of the material production technology, the price of the lithium iron phosphate material is further reduced, and in order to reduce the production cost of synthesizing the lithium iron phosphate anode material, a method for preparing the lithium iron phosphate material with low cost is urgently needed.
Disclosure of Invention
The invention aims to provide a preparation method of lithium iron phosphate, and aims to solve the requirement that the production cost of the existing lithium iron phosphate material needs to be reduced.
In order to achieve the purpose of the invention, the technical scheme adopted by the invention is as follows:
a preparation method of lithium iron phosphate comprises the following steps:
adding water into the rough lithium phosphate raw material, and stirring and washing to obtain washed lithium phosphate and a washing solution;
adding acid into the washed lithium phosphate for dissolving, then adding a metal salt solution, adjusting the pH value, and filtering to obtain a phosphate precipitate and a first filtrate;
adjusting the pH value of the first filtrate to 6-8, and filtering to obtain a second filtrate;
adjusting the pH value of the second filtrate to be alkaline, and filtering to obtain a pure lithium solution;
adding an iron source, a phosphorus source and a carbon source into the pure lithium solution, and mixing, drying and heating the mixture to obtain a lithium iron phosphate precursor;
and sintering the lithium iron phosphate precursor to obtain the lithium iron phosphate.
In a preferable embodiment of the present invention, the raw lithium phosphate is agitated and washed with water, and the mass ratio of the raw lithium phosphate to the water is 1 (0.5-10).
As a preferred embodiment of the present invention, the metal salt solution is a trivalent aluminum solution and/or a trivalent iron solution.
As a preferable technical scheme of the invention, the metal salt solution is added to adjust the pH to be less than or equal to 5.5.
As a preferred technical scheme of the invention, the washing solution is concentrated and then added with phosphoric acid to obtain lithium phosphate precipitate as a crude lithium phosphate raw material.
In a preferred embodiment of the present invention, when an acid is added to the washed lithium phosphate to dissolve the lithium phosphate, Li in the washed lithium phosphate is dissolved+With H in the acid+The molar ratio of (1) to (1-1.3).
In a further preferred embodiment of the present invention, the acid is at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid and oxalic acid.
In a preferred embodiment of the present invention, the iron source is at least one selected from the group consisting of ferrous carbonate, ferrous hydroxide, ferrous nitrate, ferrous oxalate, ferric hydroxide, ferric nitrate, and ferric citrate.
In a preferred embodiment of the present invention, the phosphorus source is at least one selected from phosphoric acid, diammonium phosphate, ammonium dihydrogen phosphate, and lithium dihydrogen phosphate.
In a preferred embodiment of the present invention, the carbon source is at least one selected from the group consisting of citric acid, malic acid, tartaric acid, oxalic acid, salicylic acid, succinic acid, glycine, ethylenediaminetetraacetic acid, sucrose, glucose, p-formylbenzoic acid, and p-hydroxybenzaldehyde.
As a preferred technical scheme of the invention, the heating pretreatment condition is that the treatment is carried out for 4 to 10 hours at the temperature of between 300 and 600 ℃.
As a preferred technical scheme of the invention, the sintering condition is sintering for 8-20 h at 600-900 ℃ under inert atmosphere.
According to research, the crude lithium phosphate generated in the waste lithium ion battery recovery field and the crude lithium phosphate generated by recovering the residual lithium from the lithium carbonate lithium precipitation mother liquor are low in price, and can be used as a raw material for synthesizing lithium iron phosphate by replacing the current lithium source. Therefore, the invention takes the low-cost crude lithium phosphate as a raw material to prepare the lithium iron phosphate. Firstly, the preparation method reduces the loss of lithium to the minimum, except that the step of adding water for stirring and washing can slightly lose lithium, the step-by-step precipitation and other steps can not cause the loss of lithium, and the recovery rate of lithium can reach more than 99 percent; in the preparation method, lithium phosphate can be generated as a raw material to continuously prepare the lithium iron phosphate, byproducts such as aluminum phosphate/iron phosphate and the like can be generated for other purposes, and the cost is saved while additional economic benefits are generated; finally, the preparation process only generates less waste liquid and waste residue, and is environment-friendly. Therefore, the method for preparing the lithium iron phosphate by using the crude lithium phosphate has the advantages of simple operation and good repeatability, the prepared lithium iron phosphate is in a nanometer scale, the 0.1C discharge gram capacity of the prepared lithium iron phosphate can reach more than 157mAh/g, the 1C discharge gram capacity of the prepared lithium iron phosphate can reach 138mAh/g, the median voltage is more than 3.35V, and the prepared lithium iron phosphate has good performance.
Drawings
Fig. 1 shows the 0.1C discharge gram capacity of a button cell prepared from the lithium iron phosphate material obtained in example 1;
fig. 2 shows the 1C discharge gram capacity of the button cell prepared from the lithium iron phosphate material obtained in example 1;
fig. 3 shows the 0.1C discharge gram capacity of the button cell prepared from the lithium iron phosphate material obtained in example 2;
fig. 4 shows the 1C discharge gram capacity of the button cell prepared from the lithium iron phosphate material obtained in example 2;
fig. 5 shows the 0.1C discharge gram capacity of the button cell prepared from the lithium iron phosphate material obtained in example 3;
fig. 6 shows the 1C discharge gram capacity of the button cell prepared from the lithium iron phosphate material obtained in example 3;
fig. 7 shows the 0.1C discharge gram capacity of the button cell prepared from the lithium iron phosphate material obtained in example 4;
fig. 8 shows the 1C discharge gram capacity of the button cell prepared from the lithium iron phosphate material obtained in example 4;
fig. 9 shows the 0.1C discharge gram capacity of the button cell prepared from the lithium iron phosphate material obtained in example 5;
fig. 10 shows the 1C discharge gram capacity of the button cell prepared from the lithium iron phosphate material obtained in example 5;
fig. 11 shows the 0.1C discharge gram capacity of the button cell prepared from the lithium iron phosphate material obtained in example 6;
fig. 12 shows the 1C discharge gram capacity of the button cell prepared from the lithium iron phosphate material obtained in example 6.
Detailed Description
In order to make the objects, technical solutions and technical effects of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described, and the embodiments described below are a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art without any inventive step in connection with the embodiments of the present invention shall fall within the scope of protection of the present invention. Those whose specific conditions are not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer; the reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
In the description of the present invention, it should be understood that the weight of the related components mentioned in the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, it is within the scope of the disclosure that the content of the related components is scaled up or down according to the embodiments of the present invention. Specifically, the weight in the embodiment of the present invention may be a unit of mass known in the chemical field such as μ g, mg, g, kg, etc.
In addition, unless the context clearly uses otherwise, an expression of a word in the singular is to be understood as encompassing the plural of the word. The terms "comprises" or "comprising" are intended to specify the presence of stated features, quantities, steps, operations, elements, portions, or combinations thereof, but are not intended to preclude the presence or addition of one or more other features, quantities, steps, operations, elements, portions, or combinations thereof.
The embodiment of the invention provides a preparation method of lithium iron phosphate, which comprises the following steps:
s1, adding water into the crude lithium phosphate raw material, and stirring and washing to obtain washed lithium phosphate and a washing solution;
s2, adding acid into the washed lithium phosphate for dissolving, then adding a metal salt solution, adjusting the pH value, and filtering to obtain a phosphate precipitate and a first filtrate;
s3, adjusting the pH value of the first filtrate to 6-8, and filtering to obtain a second filtrate;
s4, adjusting the pH value of the second filtrate to be alkaline, and filtering to obtain a pure lithium solution;
s5, adding an iron source, a phosphorus source and a carbon source into the pure lithium solution, and mixing, drying and heating the mixture to obtain a lithium iron phosphate precursor;
and S6, sintering the lithium iron phosphate precursor to obtain the lithium iron phosphate.
The invention prepares lithium iron phosphate by using low-cost crude lithium phosphate as a raw material. Firstly, the preparation method reduces the loss of lithium to the minimum, except that the step of adding water for stirring and washing can slightly lose lithium, the step-by-step precipitation and other steps can not cause the loss of lithium, and the recovery rate of lithium can reach more than 99 percent; in the preparation method, lithium phosphate can be generated as a raw material to continuously prepare the lithium iron phosphate, byproducts such as aluminum phosphate/iron phosphate and the like can be generated for other purposes, and the cost is saved while additional economic benefits are generated; finally, the preparation process only generates less waste liquid and waste residue, and is environment-friendly. Therefore, the method for preparing the lithium iron phosphate by using the crude lithium phosphate has the advantages of low cost, simple operation and good repeatability, the prepared lithium iron phosphate is in a nanometer scale, the 0.1C discharge gram capacity of the prepared lithium iron phosphate can reach more than 157mAh/g, the 1C discharge gram capacity of the prepared lithium iron phosphate can reach more than 138mAh/g, the median voltage is more than 3.35V, and the prepared lithium iron phosphate has good performance.
It should be noted that, although the steps S1-S6 describe the preparation process of lithium iron phosphate in a specific order, it is not required that the steps are performed in the specific order, and the steps may be performed simultaneously or sequentially according to actual situations.
Water is added for agitation washing to remove water-soluble impurities in the crude lithium phosphate, and in some embodiments, the mass ratio of the crude lithium phosphate to water is controlled to be 1 (0.5-10). Through optimizing the addition of water, when getting rid of water-soluble impurity as far as possible, also avoid causing the extra loss of lithium owing to adding too much water, help promoting the rate of recovery of lithium.
In order to further improve the lithium recovery rate, the washing solution obtained in S1 was concentrated, and then phosphoric acid was added to obtain a lithium phosphate precipitate, which was used as a crude lithium phosphate raw material in S1.
The concentration of the washing solution may be a common concentration method in the art, and membrane concentration is preferred to prevent additional loss of lithium.
In some embodiments, the molar ratio of phosphoric acid to lithium in the wash solution is 1 (2.7-3.3). The phosphoric acid is added to precipitate lithium in the washing liquid in the form of lithium phosphate so as to avoid the loss of lithium, so that the addition of excessive phosphoric acid can be avoided while ensuring that lithium is completely precipitated by optimizing the molar ratio of the phosphoric acid to the lithium, and the adverse effect is brought to subsequent phosphorus removal.
The invention utilizes the characteristic that lithium phosphate is soluble in acid, and can achieve the aim of dissolving lithium phosphate to form solution by adding acid. In some embodiments, the added acid is selected from at least one of nitric acid, hydrochloric acid, sulfuric acid, oxalic acid. By using the acid to dissolve lithium phosphate, new impurities cannot be introduced into the synthesized lithium iron phosphate material, most of the impurities can be automatically removed through a subsequent treatment process even if part of the impurities are introduced, and the performance of the lithium iron phosphate material cannot be influenced by the rest part of the impurities.
By optimizing the amount of the added acid, the lithium phosphate can be fully dissolved, and the problem that the pH value of the solution is too low and the subsequent reaction is not facilitated due to the addition of too much acid is avoided. Thus, in some embodiments, the molar ratio of lithium to acid H in the washed lithium phosphate is 1 (1-1.3).
The step-by-step impurity removal step is one of the key steps of the invention. Through the step-by-step impurity removal, impurities such as phosphorus, metal ions and the like in the solution can be removed, and the additional loss of lithium can be avoided. Therefore, the invention comprises the first step of removing impurities step by step: the metal salt solution is added first to adjust the pH. The phosphorus in the solution can be separated out in a form of precipitation by adding the metal salt solution, and the precipitate can be used as a byproduct for other purposes after being stirred and washed by adding water; the stirred filtrate can be returned to S1 to be used as deionized water for recycling.
In some embodiments, the metal salt solution is selected from a trivalent aluminum salt solution and/or a trivalent iron salt solution, and the precipitate formed accordingly is aluminum phosphate or iron phosphate. Preferably, the trivalent aluminum salt solution is selected from at least one of soluble trivalent aluminum salts such as aluminum nitrate, aluminum sulfate, aluminum chloride, and the like; the ferric salt solution is at least one selected from soluble ferric salts such as ferric nitrate, ferric sulfate and ferric chloride.
Adjusting the pH within a suitable range will favor the formation of a precipitate, and therefore, the pH of the present invention after the addition of the metal salt solution is controlled to be 2.0 to 5.5, it should be noted that the actual range of pH will depend on the salt solution added. Preferably, when the metal salt solution to be added is a trivalent aluminum solution, the pH should be controlled to 4.7 to 5.5.
The invention comprises a second step of removing impurities step by step: the pH of the solution is adjusted to 6-8 to remove residual phosphorus in the solution and metal ions in the previously added metal salt solution. Wherein, the residual phosphorus is removed in the form of lithium phosphate precipitate, and the lithium phosphate precipitate obtained at this time can be used as the crude lithium phosphate raw material of the preparation method S1 of the present invention for preparing lithium iron phosphate.
When the previously added metal salt solution is a trivalent aluminum salt solution and/or a trivalent iron salt solution, and correspondingly, in the second step of the stepwise impurity removal process, the removed metal ions are aluminum ions and/or iron ions, which respectively form precipitates of aluminum phosphate or aluminum hydroxide, iron phosphate or iron hydroxide, which may also be by-products of the present invention after washing and drying.
The third step of the invention comprises the step-by-step impurity removal: and adjusting the pH of the solution to be alkaline to remove impurities such as calcium, magnesium and the like in the solution, thereby obtaining the high-purity lithium solution. Wherein, the obtained impurities such as calcium, magnesium and the like are washed by water and then are subjected to solid waste treatment, and the obtained filtrate is returned to S1 to be recycled as deionized water. In some embodiments, adjusting the pH to basic is specifically adjusting the pH to 10-13.
Preferably, when the pH of the solution is adjusted to be more than 10 and less than 12, since the impurities of calcium, magnesium, etc. in the solution are not completely precipitated, the remaining impurities of calcium, magnesium, etc. may be sufficiently precipitated and removed by adding a metal chelating agent. Optionally, the metal chelator is EDTA. When the pH value of the solution is adjusted to 12-13, impurities such as calcium, magnesium and the like in the solution are completely precipitated, so that an additional metal chelating agent is not required.
And appropriate iron source, phosphorus source and carbon source are added into the pure lithium solution, which is favorable for forming lithium iron phosphate with excellent performance. Thus, in some embodiments, the iron source may be selected from at least one of ferrous carbonate, ferrous hydroxide, ferrous nitrate, ferrous oxalate, ferric hydroxide, ferric nitrate, ferric citrate; the phosphorus source can be at least one of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate and lithium dihydrogen phosphate; the carbon source can be at least one selected from citric acid, malic acid, tartaric acid, oxalic acid, salicylic acid, succinic acid, glycine, ethylene diamine tetraacetic acid, sucrose, glucose, p-formylbenzoic acid, and p-hydroxybenzaldehyde. Preferably, after an iron source, a phosphorus source and a carbon source are added into the pure lithium solution, ball milling is carried out for 10-20 h, so that the materials are fully and uniformly mixed, the completion of subsequent reaction is facilitated, and nano-scale lithium iron phosphate is generated.
The obtained lithium iron phosphate material has better electrochemical performance by crushing and secondary sintering the powder. Therefore, in some embodiments, after adding the iron source, the phosphorus source and the carbon source into the pure lithium solution and mixing, the pure lithium solution can be placed in a forced air drying oven and dried for 10 hours to 20 hours at the temperature of 80 ℃ to 300 ℃ to obtain powder; crushing the powder, placing the powder in an atmosphere furnace, and pretreating at 300-600 ℃ for 4-10 h to obtain a lithium iron phosphate precursor; and placing the lithium iron phosphate precursor in a nitrogen furnace, and sintering at the temperature of 600-900 ℃ for 8-20 h to obtain the lithium iron phosphate.
In order to clearly understand the details of the above-described implementation and operation of the present invention for those skilled in the art and to significantly embody the advanced performance of the embodiments of the present invention, the above-described technical solution is illustrated by a plurality of embodiments below.
The results of examination of the crude lithium phosphate starting material used in the following examples of the present invention are shown in table 1.
TABLE 1 crude lithium phosphate raw Material content of each element
Example 1
S1, 100g of crude lithium phosphate is taken and washed for 2 times by deionized water (or filtrate 2/filtrate 3) to remove soluble impurities in the crude lithium phosphate, and 300g of deionized water is used for stirring and washing for 30min each time. Filtering to obtain a filtrate 1 and filter residue 1; adjusting the molar ratio of 1 phosphorus to lithium in the filtrate to 1:3 by using a sodium phosphate solution, concentrating to about one tenth, separating out lithium phosphate, returning to S1, treating the filtrate by using waste liquid, and returning the steam condensate to S1;
s2, diluting the nitric acid with the concentration of 68% to the concentration of 48%, and stirring and dissolving the filter residue 1 in 327g of prepared nitric acid solution to obtain a solution 1; adding 280g of ferric nitrate nonahydrate into the solution 1, adjusting the pH to 3-4 by using ammonia water, and filtering to obtain filter residue 2 (more than 90% of phosphate ions are precipitated in a ferric phosphate form);
s3, adjusting the pH value of the solution to 6-8 by ammonia water, and filtering to obtain filter residue 3 (precipitating residual phosphate ions in the form of lithium phosphate);
s4, adjusting the pH value of the solution to 12-13 by ammonia water, and filtering to obtain filter residue 4 (impurities such as calcium, magnesium and the like are removed in the form of hydroxide precipitate) and high-purity lithium liquid; washing the filter residue 2 with water, stirring and washing for 3 times, each time for 30min to obtain a filtrate 2 and iron phosphate, drying to obtain an iron phosphate finished product, returning the filtrate 2 to the first step to be recycled as deionized water, returning the filter residue 3 to the first step to be washed, washing the filter residue 4 with water once to treat the filter residue with solid waste, and returning the obtained filtrate 3 to the first step to be used;
s5, concentrating the solution 2 to a solution with the mass fraction of Li of 5%, and adding the solution in a molar ratio of Li: p: fe: c1: 0.97: 0.95: adding phosphoric acid, ferrous carbonate and citric acid in a proportion of 0.6, performing ball milling for 10 hours, placing in an air-blast drying oven for drying for 10 hours at the temperature of 80 ℃ to obtain powder, crushing the powder by using crushing equipment, placing in an atmosphere furnace, and performing pretreatment for 4 hours at the temperature of 300 ℃ to obtain a lithium iron phosphate precursor;
and S6, placing the lithium iron phosphate precursor in a nitrogen furnace, and sintering at 600 ℃ for 8h to obtain the nano lithium iron phosphate.
Example 2
This example is substantially the same as example 1 except that in S2, 260g of aluminum nitrate nonahydrate was used in place of iron nitrate nonahydrate, and the pH was adjusted to 4.7 to 5.0; in S5, the iron source is selected from ferrous hydroxide, the phosphorus source is selected from diammonium hydrogen phosphate, the carbon source is selected from malic acid, the ball milling time is 20h, the drying temperature is 300 ℃, and the drying time is 20 h.
Example 3
This example was substantially the same as example 1 except that in S2, lithium phosphate was dissolved in 610g of 20% dilute sulfuric acid and iron nitrate nonahydrate was replaced with 195.5g of iron sulfate nonahydrate and the pH was adjusted to 3 to 4; in S5, the iron source is selected from ferrous nitrate, the phosphorus source is selected from ammonium dihydrogen phosphate, the carbon source is selected from tartaric acid, the ball milling time is 15h, the drying temperature is 150 ℃, and the drying time is 15 h.
Example 4
This example is substantially the same as example 1 except that in S2, 119g of aluminum sulfate was used in place of the ferric nitrate nonahydrate, and the pH was adjusted to 4.7 to 5.0; in S5, the iron source is selected from ferrous oxalate, the phosphorus source is selected from lithium dihydrogen phosphate, the carbon source is selected from oxalic acid, the high-temperature pretreatment temperature is 600 ℃, and the treatment time is 10 hours.
Example 5
This example is substantially the same as example 1 except that in S2, 112.5g of ferric chloride was used in place of ferric nitrate nonahydrate and the pH was adjusted to 3 to 4; in S5, the iron source is selected from ferric hydroxide, the phosphorus source is selected from phosphoric acid, and the carbon source is selected from salicylic acid; in S6, the high-temperature sintering temperature is 900 ℃, and the sintering time is 20 h.
Example 6
This example is substantially the same as example 1 except that in S2, 92.5g of aluminum chloride was used in place of iron nitrate nonahydrate and the pH was adjusted to 4.7 to 5.0; in S5, the iron source is selected from ferric nitrate and the carbon source is selected from succinic acid; in S6, the high-temperature sintering temperature is 700 ℃, and the sintering time is 15 h.
Through calculation, the lithium content in the concentrated filtrate 1, the lithium content in the ferric phosphate precipitate and the lithium contained in the solid waste are not higher than 0.2%, the lithium content in the ferric phosphate precipitate and the solid waste is lower than 0.5%, the total loss rate of lithium is lower than 0.7%, and the total recovery rate of lithium is higher than 99.3% (as shown in table 2).
TABLE 2 lithium recovery rates of lithium iron phosphates obtained in examples 1 to 6
The lithium iron phosphate materials obtained in examples 1 to 6 were used as the positive electrode material of the lithium ion batteries to assemble button batteries, the lithium iron phosphate materials were used as the positive electrode, the metal lithium plate was used as the negative electrode, the CR2032 button battery case and the like were used to make CR2032 type button batteries, and the performance test results of the button batteries obtained are shown in table 3 and fig. 1 to 12.
Table 3 test results of button cell performance using lithium iron phosphate materials obtained in examples 1 to 6
In conclusion, the invention takes the low-cost crude lithium phosphate as the raw material, the loss of lithium is reduced to the minimum by steps of fractional precipitation and the like, the recovery rate of lithium is more than 99 percent, the aluminum phosphate/aluminum phosphate obtained in the preparation process is taken as a byproduct, and the filtrate can be recycled as the raw material or deionized water, thereby further reducing the loss of lithium. In addition, the preparation process only generates less waste liquid and waste residue, and is environment-friendly.
The preparation method of the lithium iron phosphate has the advantages of simple operation and good repeatability, the prepared lithium iron phosphate is in a nanometer scale, the 0.1C discharge gram capacity of the lithium iron phosphate can reach more than 157mAh/g, the 1C discharge gram capacity of the lithium iron phosphate can reach 138mAh/g, the median voltage is more than 3.35V, and the lithium iron phosphate has good performance.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A preparation method of lithium iron phosphate is characterized by comprising the following steps:
adding water into the rough lithium phosphate raw material, and stirring and washing to obtain washed lithium phosphate and a washing solution;
adding acid into the washed lithium phosphate for dissolving, then adding a metal salt solution, adjusting the pH value, and filtering to obtain a phosphate precipitate and a first filtrate;
adjusting the pH value of the first filtrate to 6-8, and filtering to obtain a second filtrate;
adjusting the pH value of the second filtrate to be alkaline, and filtering to obtain a pure lithium solution;
adding an iron source, a phosphorus source and a carbon source into the pure lithium solution, and mixing, drying and heating the mixture to obtain a lithium iron phosphate precursor;
and sintering the lithium iron phosphate precursor to obtain the lithium iron phosphate.
2. The method for preparing lithium iron phosphate according to claim 1, wherein the raw lithium phosphate is agitated and washed with water, and the mass ratio of the raw lithium phosphate to the water is 1 (0.5-10).
3. The method for preparing lithium iron phosphate according to claim 1, wherein the metal salt solution is a trivalent aluminum solution and/or a trivalent iron solution.
4. The method for preparing lithium iron phosphate according to claim 1, wherein the pH is adjusted to 5.5 or less by adding the metal salt solution.
5. The method for preparing lithium iron phosphate according to any one of claims 1 to 4, wherein the washing solution is concentrated and then phosphoric acid is added to obtain a lithium phosphate precipitate as a raw material of crude lithium phosphate.
6. The method for producing lithium iron phosphate according to any one of claims 1 to 4, wherein when the washed lithium phosphate is dissolved by adding an acid, Li in the washed lithium phosphate+With H in the acid+The molar ratio of (1) to (1-1.3).
7. The method for producing lithium iron phosphate according to claim 6, wherein the acid is at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid and oxalic acid.
8. The method for preparing lithium iron phosphate according to any one of claims 1 to 4 or 7, wherein the iron source is at least one selected from the group consisting of ferrous carbonate, ferrous hydroxide, ferrous nitrate, ferrous oxalate, ferric hydroxide, ferric nitrate and ferric citrate; and/or the presence of a gas in the gas,
the phosphorus source is selected from at least one of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate and lithium dihydrogen phosphate; and/or the presence of a gas in the gas,
the carbon source is at least one selected from citric acid, malic acid, tartaric acid, oxalic acid, salicylic acid, succinic acid, glycine, ethylene diamine tetraacetic acid, sucrose, glucose, p-formylbenzoic acid and p-hydroxybenzaldehyde.
9. The method for preparing lithium iron phosphate according to any one of claims 1 to 4 or 7, wherein the heating pretreatment is carried out at 300 ℃ to 600 ℃ for 4 hours to 10 hours.
10. The method for preparing lithium iron phosphate according to any one of claims 1 to 4 or 7, wherein the sintering is carried out under an inert atmosphere at a temperature of 600 ℃ to 900 ℃ for 8 hours to 20 hours.
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